1. Field of the Invention
The invention relates to a process for preparing a blazed holographic optical component for a pickup that reproduces optically recorded information, and particularly to a process for effectively preparing blazed holograms having a serrated cross section.
2. Description of the Prior Art
Heretofore, a transmission diffraction grating providing on the surface grooves of a serrated cross-section is known as a blazed hologram, for components for hologram pickup (U.S. Pat. No. 3,680,945; "High-efficiency blazed grating couplers" Applied Physics Letters, Vol. 29, No. 5, 1, Sept. 1976; "Control of shape of groove for holographic grating" Applied Physics, Vol. 45, No. 7 (1976)).
The grooves of serrated cross section in blazed holograms are formed to improve photo utilization efficiency, which is reported by the report of "Efficiency Holographic Optical Head for CD Players" at Lecture Meeting of 48th Applied Physics Meeting.
The blazed hologram as above-mentioned is prepared conventionally in the following manner, a photo resist resin is first coated on a glass plate or a transparent plastic plate, and is then etched to have a serrated cross section. Further conventional method is that a rubber material is layered over the; obtained blazed hologram for its replication (U.S. Pat. No. 3,680,945).
However, the blazed holograms obtained by such methods using resist resin or rubber material were not sufficient in shape-stability and durability of diffractive function.
Recently, another method has been performed whereby a glass plate or transparent plastic plate is directly etched to be serrated on the surface for providing blazed holograms. The method will be further detailed hereunder.
A glass substrate 21 is first washed (FIG. 5(a)) and coated with a photosensitive material such as a photo resist 22 (FIG. 5(b)), which is then exposed by the two-beam interference method or an electron beam drawing method and developed to form a blazed resist pattern 22 (FIGS. 5(c) and (d)). Then, the resulting glass substrate 21 is etched to afford a blazed hologram 23 (FIG. 5(e)).
Alternatively, a glass substrate is washed (FIG. 6(a)) and applied with a photosensitive material for photo resist 22 (FIG. 6(b)), which is exposed to light through a photo mask 24 (FIG. 6(c)). Then, the photo resist 22 is developed to form a rectangular cross section (FIG. 6(d)) and the resulting glass substrate is etched by slantwise irradiation of an ion beam such as Ar gas (FIG. 6(e)) to afford a blazed hologram 23 having serrated cross section (FIG. 6(f)).
In case that transparent plastic plate is used, the hologram is similarly prepared by the abovesaid manner.
However, the conventional methods require many steps for obtaining blazed hologram 23, and thereby take a longer time in working as a whole, so that there is a problem that the price per finished blazed hologram is comparatively expensive.